Reinforcing bar



July 20, 1943. Y J. D TTTTT ES 2,324,651-

. Patented July 20, 1943 UNITED STATES" PATENT OFFICE v N.Y.

AppucationlFoeln'cxjtz-flzgzir: No. 62,173

This invention relates to improvements in reinforcing bars, and more particularly to a twisted bar used in the reinforcement of concrete.

An object of this invention is to provide an improved solid, twisted reinforcing bar.

Another object of this invention is to provide a solid twisted reinforcing bar having a relatively high yield point and relatively low fiber stress.

Still another object of this invention is to provide a twisted reinforcing bar having a large eifective bond area.

An additional object of this invention is to I form a reinforcing bar having an extremely high compression strength.

A further object of this invention is to provide a solid twisted reinforcing bar which may be twistedand stretched in a continuous process.

A more specific object of this invention is to provide a solid reinforcing bar which will not substantially change length when twisted and stretched. v

A final object of my invention is to provide a solid twisted reinforcing bar which is cheaper and more easy to manufacture than inferior bars now known to the art.

Other objects will be in part obvious from the annexed drawing and in part indicated in connection therewith by the following analysis of this invention.

This invention accordingly consists in the features of construction, combination of parts and in the unique relation of the members and the relative proportioning and disposition thereof, all as more completely outlined herein.

To enable others skilled in this art so fully to comprehend the underlying features of this invention that they may embody the same by the numerous modifications in structure and relation contemplated by this invention, a drawing de-.

picting a preferred form has been annexed as part of this disclosure, andin such drawing:

- III-III of Fig. 1; and

Fig. 4 is a cross-sectional view along the line IV-IV of Fig. 2.

Figs. 1 and 3 illustrate a preferred shape of bar to be used in the present-invention, before it is twisted and stretched. It will be readily seen that this bar generally consists of two spaced outer circular bars I and an inner circular core I to which the outer bars are connected by means of narrow webs I so as to form the complete integral reinforcing bar. A series of transverse ribs 4, spaced at equal intervals along the length ofv the bar and interconnecting the outer bars I,

the inner core 2 and the webs 3 may be provided to increase the bonding strength of the bar as a actual stretching of the outer bars I, with a stressing of the outer fibers beyond the elastic limit with a resultant raising of the yield point,

a higher modulus of elasticity and a higher compressive strength than ordinary reinforcing bars, the cross-sectional area of the individual bars will not change since, for reasons to be discussed in more detail hereinafter, the length of the bar does not change, even though the bar is not rigidly held at its ends during the twisting and stretching operation.

The advantages of twisting concrete reinforcing bars are, in themselves, generally known to the art. In the case of single solid bars, however, such as a square bar, a circular bar, or an oval bar, the twisting is accompanied by an increase in length, resulting in an undesired decrease in the cross-sectional area of the bar.

} This disadvantage was overcome to a certain extent by the use of a pair of separate twisted bars, which type of barwill be shortened in length when twisted, but which can be stretched by holding the bar rigidly at its end so that a shortening of the bar is thereby prevented, while at the same time the outer fibers are stressed so as to raise the effective yield point. -Such a bar is disclosed, for example, in the U. S. patent to Hoifmann 1,692,505. An improvement on the Hoflfmann bar is disclosed in my prior Patent 2,256,060, issued September 16, 1941, in which a greater amount of material can be twisted with resultant lower stresses on the outer fibers, than in the ordinary twisted reinforcing bar, but here again it is necessary to rigidly hold the bar at its ends to prevent shortening of the same during the twisting operation. The bar in accordance with the present invention retains all of the advantages of the bar described and claimed in my aforementioned previous patent, but has the further advantage that it needs not be rigidly held at its end in a large machine during the twisting and stretching operation, but can merely I ,be fed through a single twisting machine in a continuous operation and, contrary to previous twisted. bars of this type, will not shorten in length hor, as contrasted with a single bar previously discussed, will it increase in length. The great advantage of being able to form such a twisted reinforcing bar in a continuous operation without a shortening or a lengthening of the bar, is brought about by the fact that the bar of the present invention contains a central core, similar to a single bar, in combination with a pair of bars equally spaced from the axis of the core, and integrally interconnected with the core by means of a narrow web. In a bar of this character, the central core, upon twisting, tends to lengthen in a manner previously discussed, while the two outer bars, upon twisting, tend to shorten unless they are rigidly held at their ends.

By properLy proportioning the cross-sectional area of the inner core and the cross-sectional areas of the outer bars integrally connected with the core, the tendency of the inner bar to lengthen and the tendency of the outer bars to shorten can be effectively balanced so that any unit length of the resultant twisted bar will be substantially equal to the same unit length of untwisted bars. The exact proper proportioning may be determined experimentally and, in the light of the above discussion, it will be seen that there are two limitations to be considered. If the diameter of the central core approaches thr thickness of the interconnecting web, the be will act as two bars joined together with a web as disclosed in my prior above-identified patent, and the reinforcing bar as a whole will then shorten when twisted. On the other hand, if the area of the inner core is greater than the cross-sectional area of the outer bar, the effect of this large central area will cause an increase in length of the reinforcing bar, as a whole, when twisted. Experiments have shown that for best results to obtain an effective balance of stresses,

- and thus prevent either shortening or lengthening of the bar as a whole, the diameter of the central core should be one and one-half times the thickness of the web, or greater. The web may be as thin as rolling conditions permit. In an ideal bar, on the other hand, the outer bars will be twice the diameter of the inner core. These are approximately the proportions of the bar illustrated in Fig. 3. If the proportions indicated are followed, the unit compressive stresses on" the inner core are balanced by the unit tensile stresses on the outer bars. At the same time, the provision of a large amount of material spaced from the center of twist, as discussed, for example, in my Patent 2,256,060, previously referred to is retained.

While, theoretically, the cross-sectional area of the inner core, sufficient to counteract the tendency of the outer bars to shorten need not be as relatively large as has been illustrated in the drawing, as a practical matter for constructional reasons in the design of the twisting machine itself, the inner core will generally be made larger than necessary, in somewhat the proportion illustrated. This merely adds to the compressive strength of the inner core and the tendency of the outer bars to shorten will be only more strongly resisted.

As previously stated, rib I may be spaced longitudinalLv along the length of the bar to assist in preventing rupture between the individual bar sections and the interconnecting web during the twisting operation.

While the reinforcing bar illustrated is shown as having the inner core and the outer bars all of substantially circular cross-section, it is to be understood that my invention is not confined to bars having this particular configuration. The exact shape of the inner core and the outer bars is wholly unimportant so long as the relative cross-sectional area of the center core to the outer bars is such as to prevent a shortening of the bar as a whole due to the tendency of the outer bars to shorten during twisting.

Additionally, while I have illustrated only two outer bars spaced from the inner core, my invention is equally applicable to a bar consisting of any number of outer sections equally spaced from an inner core, so long as the inner core is suflicient size to balance the shortening effect of the outer sections upon twisting.

Since the bar in accordance with the present invention has a greater bonding surface than.

comparative bars heretofore used, it presents an additional advantage in the provision of increased bonding strength. Additionally, since this bar will have the stiffness of an I-beam section, it will be stronger than the ordinary single bar or the bar formed by the twisting together of two independent bars.

Having described an illustrative embodiment of the invention, it is accordingly pointed out that various changes and modifications therein are contemplated, without departing from the invention as set forth in the following claims.

I claim:

1. A twisted and stretched reinforcing bar for concrete and the like, comprising a plurality of outer sections of substantially equal cross-sectional area, a center core of less cross-sectional area than any individual outer section, and relatively narrow webs integrally connecting said core with said outer sections, the cross-sectional area of said inner core being such that when said bar is twisted about the axis of said core, the unit compressive stresses on said core are substantially equal to the total unit tensile stresses on said outer sections.

2. Th combination according to claim 1, in combination with longitudinally spaced transverse ribs interconnecting said outer sections, webs and core.

3. A new article of manufacture, comprising a reinforcement bar for concrete and the like capable of being twisted about its axis and stretched in a continuous process without change in length, comprising a central core and a plurality of spaced outer sections integrally connected with said core, the cross-sectional area of said inner core being such that when said bar is twisted about its axis, the unit compressive stress on said core is substantially equal to the total unit tensile stresses on said outer sections.

4. As a new article of manufacture, a reinforcement bar capable of maintaining its original length while being twisted and stressed about its axis, without being held at both its ends.

5. A twisted and stressed reinforcement bar,

comprising a pair of bars of substantially circular cross-section equally spaced from a smaller circular bar and integrally interconnected therewith by a narrow web, said smaller bar, webs and outer bars being twisted along their length about the axis of the smaller bar.

6. The combination according to claim 5, in combination with longitudinally spaced transverse ribs interconnecting said bars and webs.

7. A twisted and stretched reinforcing bar for concrete and the like, comprising a plurality of outer sections of substantially equal cross-sectional area, a center core of less cross-sectional area than any outer section, and relatively narrow ribs integrally interconnecting said core with said, outer sections, the cross-sectional area of said inner core being such that when said bar is twisted about the axis of said core the'tendency of the outer sections to lengthen is balanced by the tendency of the inner core to shorten, where-' by the eflfective length of the bar as a whole remains substantially unchanged.

8. The combination according to claim 7, in

combination with longitudinally spaced transverse ribs interconnecting said outer sections, webs and core.

9. The combination according to claim 1, in

which the diameter of the center core is at least JOSEPH D. .STITES. 

